In virtually all portable electronic devices such as electronic timepieces, for which a very low level of power consumption is essential, integrated circuitry based on CMOS FET elements is utilized at present. Such circuit elements display various changes in their characteristics with variations in operating temperature. In particular, an increase in operating temperature results in a decrease in the threshold voltage of such an element, and a reduction in the propagation time. Such changes in characteristics can be compensated for by appropriately changing the supply voltage at which the circuitry is operated. Conversely, if the circuitry is operated at a fixed supply voltage, over a wide range of temperatures, then it will be necessary to apply an unnecessarily high level of supply voltage over a certain range of temperatures, in order to ensure satisfactory operation within some other temperature range. This results in wasteful consumption of battery power, since the minimum practicable supply voltage is not being applied to the circuitry at all times. In the case of certain portable electronic devices such as electronic timepieces, it is essential to reduce the battery consumption to as low a level as possible, in order to ensure maximum battery lifetime and to enable the timepiece size to be reduced by utilizing a battery of small dimensions (and hence relatively low capacity). There is therefore a requirement for some effective means for controlling the supply voltage applied to an electronic circuit, such as a timepiece circuit, in accordance with operating temperature, in such a way that the minimum supply voltage necessary for satisfactory operation of the circuit is provided at any temperature. Such control means is provided by the circuit of the present invention.